1. Field of the Invention
This invention relates to activation of aluminum particles. More particularly, it relates to monitoring the production of an active particulate aluminum by improved milling. By aluminum, I mean aluminum and aluminum base alloys containing at least 50% by weight aluminum.
2. Description of the Prior Art
Particulate aluminum or aluminum powder, for example, atomized powder, is sometimes milled in an inert atmosphere in the presence of inert hydrocarbons such as hexane, kerosene, benzene, mineral spirits and the like, to avoid excessive formation of an oxide-coated surface and to produce aluminum which will combine under pressure with hydrogen gas and an olefin such as ethylene or isobutylene to form an alkylaluminum compound. Aluminum milled in this way, however, does not always exhibit the required degree of activity, perhaps because of the formation of conglomerates of small particles welded and pounded together in a manner which prevents formation of the desired amount of fines of small particle size and of sufficient surface area and low oxide content. Therefore, finding a method of ensuring production of an active or pyrophoric aluminum consistently sufficiently reactive to form further useful products such as, for example, alkylaluminum compounds, represents a highly desirable result.
In my parent U.S. Pat. No. 3,890,166, previously referred to above, I disclose and claim milling particulate aluminum in the presence of a material (which I called a milling aid) that will sorb onto the surface of the aluminum sufficiently to stabilize it against rewelding but insufficietly to prevent access to the nascent aluminum surface by a reactive substance, and which thereby imparts to aluminum a high degree of activity, particularly, chemical reactivity. Highly sorptive oxygen-containing compounds of limited reactivity were found to be most efficient in preparing active aluminum according to that invention. By "highly sorptive", I mean having the capability of being easily or readily sorbed onto the surface of the aluminum particles. By "of limited reactivity", I mean of insufficient reactivity to react to produce an undesirable new compound in bulk during the milling. The milling aid disclosed and claimed therein must be so constructed or made up that it sorbs onto the surface of the particulate aluminum during milling just enough to protect it adequately in the mill, that is, just enough to promote comminution rather than welding of particles, but can be displaced by another material or otherwise allow access to the nascent aluminum after completion of the milling. It should leave sites of nascent aluminum intermingled with sorbed sites.
It was further pointed out that milling time is significant only insofar as milling does not continue beyond the time required to generate enough new surface to sorb the milling aid available in the mill, as total utilization of the milling aid causes an active milling environment to revert to an inactive environment, and welding rather than comminution begins to predominate.